Building batteries that go beyond lithium

New Zealand researchers are developing alternative batteries from common material to go beyond lithium, skipping the solar cell and downsizing monster redox-flows.

In today’s tech-hungry world, lithium batteries are ubiquitous. Everything from your mobile phone to the neighbour’s electric car rely on the metal, and it’s easy to see why. Lithium-ion batteries pack a serious punch, storing more energy than any other battery of equivalent size, and delivering power to where it’s needed, quickly and efficiently.

But did you know that they’re hardly ever recycled? The complexity and high cost of recovering materials from lithium-ion batteries means that, in the EU, 95% of them are either incinerated at their end-of-life, or end up in landfill. And Australian consumers recycle just 2% of the lithium-ion batteries they buy. It’s not as if the raw materials needed to make them – namely lithium and cobalt – are easy to find. Thanks to an ever-growing demand, pressure on their supplies have never been higher, and that’s before we consider the significant environmental impact of metal mining. Extracting one tonne of lithium requires more than two thousand tonnes of water, and a study of soil samples in a cobalt-mining region of southern Congo concluded that it was “among the ten most polluted areas in the world.”

It’s clear that something has to change. For MacDiarmid Institute‘s former director, Professor Thomas Nann, that ‘something’ is battery chemistry, and his solution is a very familiar metal – aluminium.

“Aluminium is similar to lithium in a key way – aluminium’s potential energy density (a measure of how much energy a material can store) is very, very close to lithium’s. But unlike lithium, aluminium is the third most abundant element in the Earth’s crust,” he says. Nann and his team took that as a starting point and set out to design a new aluminium-ion battery.

They wanted to stick with a familiar battery design – namely, two electrodes separated by an electrolyte – but everything else was up for grabs. Their first target was the electrolyte material itself which, because it carries the ions that make the battery work, can have a big impact on its performance. The best battery electrolytes are usually made from an expensive cocktail of compounds, so in search of a cheaper alternative, Nann and MacDiarmid-funded PhD student, Nicolò Canever looked to those already working with aluminium.

“It turns out that the mining industry was already studying a compound called acetamide, used to recover aluminium from minerals,” Nann explains, “and because acetamide can be produced by bacteria or plants, it is incredibly inexpensive.” That formed the basis of their new electrolyte, and in performance tests, it compared favourably to existing compounds but could be made for a fraction of the cost.

This work was published in a prestigious Royal Society of Chemistry journal in September, but the team’s design of a new electrode material took a different route. Nann’s PhD student, Shalini Divya had a challenge on her hands – rather than simply improving on what had gone before, her aim was to start from scratch, and rethink what she knew about electrodes. “In the end, Shalini found a material that outperforms everything that’s been published to date,” says Nann, “It is so transformative and so surprising that we’re now trying to commercialise it.”

A key step in the patenting process is to prove that lab-produced batteries could also be manufactured on commercial equipment, but that capability doesn’t yet exist here in New Zealand. So, funded by MacDiarmid, Nann and Divya travelled to Germany’s Fraunhofer Institute. There, they used the lab’s world-class facilities to make 20 of their novel aluminium-ion batteries and brought them back to New Zealand for testing. The results have been hugely promising, with Nann saying that they’re now “approaching the performance of lithium-ion batteries already on the market.” Best of all, their batteries could be produced with only very minor changes to existing processes “which is a key consideration for potential investors and manufacturers.”

Nann (who is now based at University of Newcastle, Australia) says the need for sustainable energy storage has never been more urgent. “As we transform into an energy landscape dominated by renewables, the problem is not getting hold of energy – after all, if we covered 250 by 250km2 of the Australian outback in commercial solar panels, we’d generate all the energy our entire planet needs,” he explains. “This isn’t as much area as it initially seems – rows of solar panels alongside existing highways could make a big impact.”

Can we skip the solar cell altogether, though?

Doctor Aaron Marshall.

Another battery project connects Nann with MacDiarmid researchers at the University of Canterbury. One of the collaborators, Dr Aaron Marshall says the project is funded under MBIE Smart Ideas, and involves looking at new smart materials that can convert sunlight directly into stored battery energy, without needing to making electricity in the process (i.e. skipping the whole solar cell creation of electricity step).

“We’re trying to find a material which absorbs the sunlight and catalyses the charging reaction directly inside the battery.”

Marshall and his MacDiarmid collaborators are also working to speed up (and shrink) redox flow batteries. In a redox flow battery, the ‘energy’ is stored in chemicals which sit in (usually big) tanks separate to the battery itself. When energy is needed, the chemicals are pumped through the battery and through the porous electrodes.

“The concept is a bit like filling your car’s fuel tank with petrol – you could then leave the car for a year and it would still have a full tank of gas and be ready to drive when you needed it.”

And he says the chemicals are relatively abundant and therefore relatively cheap over the lifetime of the battery.

But the batteries are currently slow.

“Slow reactions means the battery requires big electrodes. And if the electrodes are large, the rest of the battery has to be large as well, and the whole thing ends up being expensive.”

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